I purchased a 1999 Suburban 1500 LT 5.7, 4wd, last week. It has a rough idle. Previous seller said spider injector replaced. In the glove box is a receipt from last January for a distributor cap and rotor and the seller said they were replaced. I took the vehicle to O'reilly's and had it scanned, and code is P0300.

I removed 1 spark plug (AC delco iridium) and no oil on it and looked in good condition. Gap @ .055, not significant enough to cause rough idle since gap should be .06.

I pulled the dipstick and oil on it looks like it had a recent oil change.

Another problem...after driving it a few days I checked the coolant in the reservoir was empty even though the level was ok before I drove it home. Also, in the glove box is a receipt for a water pump. There are no coolant leaks under the vehicle. I told the seller about it, and his reply:

"I know the dude before me replaced the water pump. Those reservoirs are for overflow. If you notice they don't have a pressurized cap on it. You should only ever add directly into the radiator on those, which is a pressure sealed cap. However, It has never ran hot or giving me any problems. So, I've never even added coolant to it." I don't think that's correct info...my understanding is the coolant is to be added in the reservoir not the radiator. Seller purchased the vehicle at the beginning of this March. He bought it for resale not for personal use.

Suggestions for troubleshooting these 2 problems?

 

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